Isomerization of normal butene



Patented on. 1,1940

f UNITED STATES PATENT OFFICE" ISOMERIZATION OF NORMAL BUTENE Charles L. Thomas and Herman S. Bloch, Chicago, 111., assignors to Universal Oil Products. Company, Chicago, 111., a corporation of Dela- No Drawing.

pplication February 9, 1939,

Serial No. 255,480

ilSClaims. romeo-ass) r This invention relates particularly to the treatment of normal butenes to transform them into isobutene.

W novel process for accomplishing this particular isomerization reaction employing particular catalysts and conditions of operation. The butenes comprise the mono-olefins' containing 4- v carbon atoms per molecule. The names of these W hydrocarbons, their structures, and boiling points reference:

Recently the butenes have become of considerable importance to the petroleum industry as a no result of the demand for high antiknook fuel suitable for use in high compression aviation engines. They occur as constituents of cracked gases formed in plants operating primarily to produce gasoline and can also be produced by the as catalytic dehydrogenation of butanes which occur in large quantities in wet natural gases and in still and tank gases of petroleum refineries. The butenes and butanesjare utilizable as such only in limited quantities on account of their relatively high vapor pressures and at the present time there is considerable over-production of them so that processes are-being developed in i The steps in preparing octanes for use as high a antihnoclr saturated aviation motor fuel consists, at the present time, in first polymerizing buten'es by either thermal or catalytic processes and then hydrogenating the resuitantoctene fractions. As

v a result ofmany investigationsit has been del terminedthat the octanes having the highest antiknock value are those which have the most compact molecules, or in other words the great-.- est branched-chain structures. Further, it has been shown that the dimers of isobutene, which correspond largely to 2,4,4-trimethyl-l-pentene More specifically this invention comprises the are given in the followingtable for purposes of r1, Name Structure igg i l-buteno -QJ. o1anor1.on=ora....Q..... -a

z-butcnacisn; HC- CHa +l-L5 H --CH: n Zhutenmtrenc RAJ-om"; +2.5 CHr-il-H a CH:

W MO-UEWQDB s em -e their more eillcient utilization.

and 2,4,4-trimethyl-2-pentene on hydrogenation yield octane fractions of considerably greater antilsnock value than do the dimers produced by the dlrectpolymerization of the normal butenes,

, or by mixed polymerization of isobutene and nor- 5 mal butenes. In actual numerical values, using 2,2,4-trimethyl pentane as a standard of refer-' .ence of 100 octane number, the hydrogenated dimers of isobutene have octane numbers of 97- 109; thoseof normal butenes from 83 to 85. and 10 hydrogenated mixed dimers from 9-0 to 9-7. These data are only approximate as it has been found that the actual values vary with the conditions of polymerization. It is obvious from the foregoing that any increase in the relative percent- .ages of isobutene in hydrocarbon gas mixtures is very desirable and it is the object of the present invention to provide a process for accomplishing this object. y

In one specific embodiment the process of the 99 present invention comprises subjecting gases containing normal butenes at elevated temperatures under atmospheric or relatively low superatmospheric pressure, to contact with catalytic materials comprising synthetically prepared calcinedmixtures of the hydrogels of silica (S102) alumina (A1203), and thoria (ThOa) for the conversion of said normal butenes into isobutene.

In the iollowingspeciflcation the term "Silicaalumina-thoria masses is used inits' broadest 9- sense. Inasmuch as the chemical knowledge of the solid state is imperfectly developed, it is not possible to give the structure of all solid sub-- stances. All that can be said definitely concerning the silica alumlna-thoria" masses isthat they contain silica, alumina, and thoria in some combination or combinations. 7 We have specitlcaliy described the catalytic masses used in the process of this invention and have arbitrarily referred tothem as silica-alumina-thoria masses. 0* for lack of a more'appropriate term.

According to the present invention. normal butenes. contained in gas mixtures, such as are 1 formed by dehydrogenation of butane, or as remain in butane-butene fractions after removal therefrom of isobutene by selective methods, such as polymerization in the presence of catalysts comprising solid phosphoric acid, sulfuric acid solutions and others, are isomerized to a substantial degree into isobutene by contact at elevated i temperatures with silica-alumina-thoria catayst The preferred isomerization catalysts may be prepared by a number of alternative methods which have certain necessary features in common [tit as will subsequently be described. Generally speaking, however, the catalysts may be considered to comprise an intimate molecular combination of silicon, aluminum, thorium, and oxygen, all of the components or which possess more or less low activity individually but display high activity in the aggregate. The activity is not an additive function, it being relatively constant for a wide range of proportions of the components whether in molecular proportions or fractions of molecular proportions. No one,component may be determined as the one component for which the remaining components may be considered as the promoters according to conventional terminology, nor can any component be determined as the support and the others as the catalyst proper.

According to one general method of preparation the preferred catalyst may be prepared by precipitating silica from a solution as a hydrogel and subsequently admixing or depositing the hydrogels of alumina and thoria upon the hydrated silica. One of the more convenient methods of preparing the silica hydro-gel is to acidify an aqueous solution of sodium silicate by the addition of an acid, such as hydrochloric acid, for example. The excess acid and the concentration of the solution in which the precipitation is brought.

about determine in some measure the suitability of the silica hydrogel for" subsequent deposition of the hydro-gels of alumina and thoria. In general, suitable hydrated silica may be produced by the use of dilute solutions of sodium silicate and the addition of a moderate excess oi acid whereby the desired active silica gel is obtained and conditions of filtering and washing are at an op accelerating hydrocarbon conversion reactions of the present character. It is possible that the presence of the alkali metal impurities causes a sin'tering or fluxing of the surfaces of the catalyst at elevated temperatures so that the porosity is much reduced with corresponding reduction in effective surface. Alkali metal ions may be removed by treating with solutions of acidic materials, ammonium salts, or salts of aluminum and thorium. When treating with acids, as for example with hydrochloric acid, the acid extracts the alkali metal impurities in the silica gel. The salts formed and acid are then substantially removed by water washing treatment. Where ammonium salts, or salts oi aluminum and thorium are used, the ammonium or multivalent metals used apparently displace the alkali metal impurities present in the composite and the alkali metal saltsformed, together with the major portion of the multivalent salts, are removed in the water washing treatment. Some of the multivalent metals introduced into the silica hydrogel in-the purifying treatment may. become a permanent part of the composite, whereas in the treatment with ammonium salts small amounts of the ammonium salts remaining after the washing process will be driven oil? in subsequent treatment at elevated temperatures.

In one of the preterred methods of compositing the hydrogel materials, the purified precipitated hydrated silica gel may be suspended in' a soluamazes tion of thorium and aluminum salts in the desired proportion and thoria and alumina hydrogels deposited upon the suspended silica hydrogel by the addition of volatile basic precipitants, such as ammonium hydroxide, for example, or ammonium carbonate, ammonium hydrosulfide, ammonium sulfide, or other volatile basic precipitants, such as organic basis, may be employed. According to this method, the purified silica gel maybe suspended in a solution of thorium nitrate and aluminum chloride. for example, and the hydrated thoria and hydrated alumina precipitated by the addition of ammonium hydroxide. In this example, the alumina and thoria are co -precipitated. A

Alternatively the purified hydrated silica gel maybe mixed while in the wet condition with separately prepared hydrated alumina and hydrated thoria precipitated either separately or concurrently as for example, by the addition of volatile basic precipitants to solutions of aluminum and thorium salts. The hydrated alumina and hydrated thoria thus prepared are substantially free from alkali metal ions and can be admixed with the purifiedsilica gel. However, if alkali metal ions are incorporated as when the hydrated alumina is prepared from sodium alums inate, for example, or if thorium tetrahydroxide is precipitated by the interaction of thorium nitrate and sodium hydroxide, regulated purification treatment and water washing, by methods selected from those described in connection with the purification of the hydrated silica gel to re= move alkali metal ions, will be required. Care should be observed in the selection and concentration of reagents used so as not ,to dissolve unduly large amounts of alumina or thoria. As further alternatives, the purified silica gel may be added to a solution. of salts of aluminum and thorium and hydrated alumina and hydrated thoria deposited by hydrolysis with or without the use elf heat, or the purified silica gel may be mixed with suitable amounts of salts of aluminum and thorium as, for example, in forming a paste and heating whereby alumina and thoria are deposited upon the silica gel as a result of the decomposition of the aluminum and thorium salts.

In the methods above described, a silica hydro gel free from alkali metal ions was admmed or had deposited thereon relatively pure hydrated alumina and hydrated thoria prior to drying treatment. In methods described below, the hydrated silica, hydrated alumina and hydrated thoria are concurrently precipitated or admixed and treated to remove alkali metal ions from the composited material prior to drying treatment either in the presence of the original reactants or subsequent to water washing. Thus-solutions of silicon compounds, more usually alkali metal silicates and soluble aluminum and thorium salts, may be mixed under regulated conditions of acidity or basicity to jointly precipitate hydrated silica, hydrated alumina, and hydrated thoria in varying proportions. For example, solutions of sodium silicate, aluminum chloride, and thorium nitrate may be mixed and alkaline or acid reagents added according to the proportions used so that a pH in the range of 3-10 is obtained. In cases where a sol is formed the precipitation may be brought about if thesol is acid by the addition of .a volatile base, as for example, ammonium hydroxide, and alkali metal salts removed by water washing, or the composite may be treated as indicated above in connection with the purification of the hydrated silica to remove alkali metal ions. :5

merization or catalytic splitting reactions producing isobutene, normal butenes, and liquid products of lower boiling points than the originally-formed polymers. In vie of the complexity of such a combination of ymerization and splitting reactions, it is obvious that the above mechanistic concept may not express the exact course oi the reactions involved; and, accordingly, the concept should not be miscon= strued so as to limit the invention.

The following numerical data are introduced to indicate some of the results obtainable in isomerizing normal butenes by the present process, although it is not intended to limit the I downwardly through a. heated tube containg 6-10 scope of the invention in strict accordance therewith:

An isomerization catalyst prepared according to 4 the process of the present invention consisted of a mass corresponding approximately to 200 moles of silica (S102), 10 moles of alumina (A1203) and 1 mole of thoria (Thor). The general procedure observed in preparing this catalyst was to precipitate silica gel, wash and treat to free it from alkali metal ions, suspend the puri- 95 fled precipitated silica in a solution of aluminum chloride and thorium nitrate, and precipitate hydrogels of alumina and thoria in the presence of the suspended silica hydrogel by the use of ammonium hydroxide.

1650 parts by weight oi a commercial grade of sodium silicate (equivalent to 8 moles of S102) was diluted with 7000 parts by weight of distilled water. A solution of hydrochloric acid (5 normal) was prepared by diluting 562 parts of concentrated (12- normal) hydrochloric acid with water to a total volume corresponding to 1350 parts. The dilute hydrochloric acid solution was added gradually to the diluted sodium silicate (stirred mechanically) which was then further diluted by the addition of 1000 parts of water. After the addition of the total quantity of the dilute acid solution, the precipitated silica hydrogel was collected on a filter, then slurried in 4000 parts of water and again filtered, this operation being repeated several times. Secondly, inv order to remove the alkali metal ions still remaining as impurities in the washed silica gel by further treatment with dilute hydrochloric acid, the silica gel was slurried in 4000 parts of water containing 40 parts of the diluted (5 normal) hydrochloric acid, the treatment being repeated twice. The precipitate was then subsequently washed several times with water, with 4000 parts by volume of an aqueous solution containing 21 parts by weight of ammonium chloride and then several times with water.

1160 parts by weight corresponding to 2.8 molecular portions of the purified silica hydrogel was suspended in 3000 parts of an aqueous solution containing 67.6 parts by weight of aluminum chloride hexahydrate (0.28 molecular portions) and 7.72 parts by weight of thorium nitrate tetrahydrate (0.014 molecular portions). To this suspension approximately 75 parts by weight of concentrated ammonium hydroxide solution was added with stilling until the reaction mixture was basic to litmus, after which the precipitated silica-alumina-thoria mass was collected on a filter. The filter cakewas dried by heating in air for approximately 16 hours at a temperature increasing gradually from 220 to 300 F. The

dried powder was then pressed and broken up to obtain approximately 6-10 mesh sized particles which were calcined in a stream of dry air at amazes approximately 900 F. ior 6 hours, during which time moisture and some ammonium chloride were expelled from the catalytic mass.

Isomerization runs were made on a drysocalled "de-isobutenized" butane-butane fraction mesh particles oi silica-alumina-thoria catalyst which had been activated by heating previously for 6 hours at 900 F, in a stream of air at atmospheric pressure. Before ,this activation treatment the particles or granules of the catalyst had been formed by pressing the powdered silica-alumina-thoria mixture into a hard cake by means of an hydraulic press, and then crushing this cake and screening the granules to the desired mesh size.

The results obtained in these laboratory scale runs showed that isomerization of normal butenes into isobutene increased with temperature rise. Also, it was found that considerable polymerization occurred at long times of contact, but

was avoided to a substantial degree at shorter times of contact. Under the heading polymerization and loss of Table 1 are included the conversions of the normal butene content of gas mixtures into heavier and lighter products. Such formation of propene and lighter gases, at the expense of the butenes, occurred to a substantial degree in other runs when pure butenes were subjected to temperature in the order of 1100 F. using low space velocities (volumes of gas per hour per volume of catalyst) in the approximate range of 20iii00.v

TABLE 1 Isomerization of normal butenes into isobutene in the presence of silioa-alumina-thmia catalyst Polymeri- Contact Space isomama- Temp, F. time. veloction. per fg g z gf seconds ity cent cent 3. 236 17. 7 41. 0; 8 885 20. ll. 0. 37 1885 18.0 9. 0. 26 2630 i6. 5 2.

After the runs at 842 F., which lasted approxi-- mately.2 hours, the catalyst was as hard as when charged, but black with acarbonaceous deposit on both the exterior and interior of the particles. It was then reactivated by heating in a stream of dry air for 6 hours at 900 F., and restored to its original white color and substantially unchanged isomerizlng' activity. Subsequent use of this reactivated catalyst at 930-940" F.,' gave the results shown in the above table.

In isomerization plants of commercial dimensions the relationship of isomerization to conditions of operation may not necessarily be the same as observed in small runs made in laboratory apparatus.

The silica-alurrdna-thoria catalyst retained its Butane isomerization life test in the presence 0] a silica-alumina-thoria catalyst Isomerization,

Time on test, hours percent 21. 9 3-4. 17. 2 16-17 19. 6 40-41.. 21. 9 68-69. 21. 7 80-81 18. 5 93-94.. 16. 5 113-114 21. 1 Average 19. 8

The foregoing specification and limited numerical data will serve to indicate the character of the process of the present invention and the nature of the results to be expected in its practice, although neither section is introduced with the idea of unduly limiting the inventions generally broad scope. r

We claim as our invention:

1. A process for' converting normal butenes into isobutene which comprises contacting said normal butenes at a temperature in the approximate range of 700-1100" F. with catalytic material comprising essentially a synthetically prepared composite mass of silica, alumina, and

- thoria.

2. A process for converting normal butenes into isobutene which comprises contacting said normal butenes with catalytic material comprising essentially a synthetically prepared composite mass of silica, alumina, and thoria, at a temperature in the approximate range [of 700-1100 F., under a pressure in the approximate order of 0.05-5.0 atmospheres. 1

3. A process of isomerizing into isobutene a substantial portion of the normal butene content of essentially i-carbon atom hydrocarbon fractions, substantially free from isobutene, which comprises contacting said hydrocarbon fractions with catalytic material comprising essentially a synthetically prepared composite mass of silica, alumina, and thoria at a temperature in the approximate range 01' 700-1100 F.

4. A process for isomerizing into isobutene a substantial portion of the normal butene content of essentially ii-carbon atom hydrocarbon fractions, substantially free from isobutene. which comprises contacting said hydrocarbon fractions under substantially atmospheric pressure with catalytic material comprising essentially a synthetically prepared composite mass of silica, alumina,- and thoria at a temperature in the approximate range of 700'-ll00 F.

5. Avprocess for isomerizing into isobutene a substantial portion of the normal butene content of essentially 4-carbon atom hydrocarbon fractions, substantially free i'rom isobutene, which comprises contacting said hydrocarbon fractions with catalytic material comprising essentially a synthetically prepared composite mass of silica, alumina, and thoria at a temperature in the approximate order of 700-1100 F. under substantially atmospheric pressure for a contact time in the approximate range of 0.01 -4.0 seconds.

6. A process for isomerizing into isobutene a substantial portion of the normal butene con- 1 tent of essentially 4-carbon atom hydrocarbon fractions, substantially free from isobutene, which comprises contacting said hydrocarbon fractions with catalytic material comprising essentially a synthetically prepared composite massoi' silica, alumina, and thoria at a temperature in the approximate range of 7004100 F., under a pressure in the approximate order of 0.05-5.0 atmospheres.

'7. A process for converting normal butenes into isobutene which comprises contacting said normal butenes under isomerizing conditions with catalytic materials comprising essentially a hydrated silica-alumina-thoria from which alkali metal ions have been removed.

8. A process for converting normal butenes into isobutene which comprises subjecting the normal butene to isomerizing conditions in the presence of a calcined mixture 0! the hydrogels of silica, alumina and thoria.

CHARLES L. THOMAS. HERMAN 8. BLOCK. 

